Since high Tg (glass transition temperature) thermoplastic resins (e.g., Tg of greater than or equal to about 180° C.) are processed at high temperatures, many standard additives that are used to flame retard other resins are unstable, decomposing under the high process temperatures needed to melt process the viscous high Tg amorphous thermoplastics. The decomposition of standard flame retardant (FR) additives during melt processing, as well as the detrimental effects such decomposition products can have upon the resin and the equipment, is a problem. This is true of amorphous polyetherimide (PEI) and polysulfone (PSU) resins that have high Tg and high viscosity making them more difficult to melt process than crystalline resins or lower Tg amorphous resins. Efforts to improve the flame retardancy of PEI by forming blends with additional materials such as brominated polycarbonate, aliphatic bominated or chlorinated compounds, and hydrated inorganic compounds like aluminum trihydrate and some alkyl phosphates, are ineffective due to decomposition or volatilization of the flame retardant additive.
A particular flame retardancy deficiency has been noted in PEI and polysulfone films having a thickness of 25 micrometers to 300 micrometers (e.g., films used in applications such as electronics). Hence, PEI and polysulfone films have need of improved flame retardant performance. These thin films have a relatively high surface area that is exposed to air, making the combustion process more favorable than in thicker sections. Electronic specifications often require the film to exhibit sufficient flame retardancy such as that specified in UL-94 (Underwriter's Laboratory Bulletin 94 entitled “Tests for Flammability of Plastic Materials, UL-94”). A rating of VTM-0 is desirable in many applications. Polyetherimide and polysulfone thin films, however, often only attain a UL-94 rating of VTM-1 or VTM-2. Various unsuccessful attempts have been made at improving the flame retardancy rating and ignition resistance of the film while retaining the melt processability, good mechanical and electrical properties, and transparency of the PEI, PSU, and polyethersulfone (PES) films. Therefore, there remains a need to produce polyetherimide and polysulfone films having a thickness of about 25 micrometers to about 300 micrometers while attaining a UL-94 rating of VTM-0.